This application claims priority from Japanese Patent Application No. 2002-313023 filed Oct. 28, 2002, which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an IC socket for the fine pitch IC package such as the CSP (Chip Size Package), more particularly to an IC socket for the fine pitch IC package such as one obtained by improving the contact structure of the IC socket for the fine pitch IC package.
2. Description of the Related Art
In the conventional IC sockets for the fine pitch IC packages such as the CPS or the like, the cylindrical contact pins elastically deformable in vertical direction have been used as contacts for electrically connecting the IC package with a test board (Refer to U.S. Pat. No. 5,727,95, Japanese Patent Application Laid-open No. 10-214649(1998), Japanese Patent Application Laid-open No. 2001-208793, etc.).
For example, the contact pin disclosed in U.S. Pat. No. 5,727,954 will be described briefly referring to FIG. 17.
As shown in FIG. 17, contact pin 101 comprises an upper pin terminal 104, a lower pin terminal 105 and a coil spring 107. The upper pin terminal 104 comprises a smaller-diameter pin terminal 104a, to be in contact with the external terminal or solder ball 117 of the IC package 116, and a larger-diameter cylindrical sleeve 104b having a bottom and opening downward. The lower pin terminal 105 comprises the smaller-diameter portion 105a, to be in contact with the contact terminal or land 115 of the external circuit such as that of the testing board 114, and the larger-diameter columnar fitting member 105b fitted so as to be movable vertically within the cylindrical sleeve 104b. Further, the coil spring 107 is placed within the cylindrical sleeve 104b to force the upper pin terminal 104 upward and the lower pin terminal 105 downward respectively. Further, the numeral 102 denotes an insulation base made from an insulating material, and each of the contact pins 101 is placed within a corresponding through-hole 103 provided with the insulation base 102.
Such a telescopic construction of the contact pin 101 permits the upper pin terminal 104 and the lower pin terminal 105 to move telescopically or vertically to each other, and the force of the coil spring 107 enables the pin terminal 104a of the upper pin terminal 104 to contact with the external terminal 117 of the IC package 116, while the pin terminal 105a of the lower terminal 105 to contact the contact terminal 115 of the test board 114 respectively with a predetermined pressure.
In recent years, as the demand for the IC packages of higher performances increases, the external terminals of such IC package are required not only to be increased in number but also to be more fine pitch. As a result, the IC packages with the external terminals pitched less than 0.4 mm have come to be developed to meet the increasing demand. As the level of the fine pitch of the external contacts of the IC package rises, naturally it becomes necessary for the IC socket to have fine pitch contacts in order to electrically connect the external terminals of the IC package with the test board in an occasion such as the long-run reliability test or screening of the IC packages.
As discussed previously, the cylindrical contact pin used for the fine pitch contact pin in the conventional IC socket comprises a cylindrical sleeve designed for containing a columnar fitting shaft and a coil spring. As the pitch of the contacts becomes shorter, it naturally becomes necessary to set the outside diameter of the cylindrical sleeve to be less than the pitch. However, the manufacture of the cylindrical sleeve having such an extremely small outside diameter requires an exquisite manufacturing technique and a considerable length of time, which leads to the rise of the unit manufacturing cost of individual cylindrical sleeves and the rise of the manufacturing cost of IC socket itself, since the recent IC socket is required to be provided with a large number of fine pitch contacts.
For instance, a contact pin structure not using the costly cylindrical sleeves has been disclosed in Japanese Patent Application Laid-open No. 2001-93634 and U.S. Pat. No. 5,414,369. In the proposed cases, the current flows through the coil spring, thereby causing the path of the current to become longer than necessary and resulting electrically adverse effects such as the development of the magnetic field around the coil spring and the increase in the resistance to the flowing current resulting in generating the heat.
The object of the present invention is to provide an IC socket for the IC package featuring the ease of manufacturing, good electrical characteristics, the contact pins designed for being vertically displaceable and suiting the fine pitch arrangement, in consideration of the above-mentioned problems of the conventional IC sockets.
In order to attain the above-mentioned object of the present invention, the IC socket for the fine pitch IC package according to the present invention comprises a socket body having an opening for guiding the IC package to a predetermined position, an insulation base having a plurality of through-holes corresponding to the external terminals of the IC package, contact pins placed in the through-holes respectively, and a cover member for applying a predetermined pressure to bring the external terminals of the IC package and the contact pins into contact with one another, wherein each of the contact pins is formed with a first plunger, including a terminal portion to be in contact with the external terminal of the IC package, a wider portion whose width is larger than the width of the terminal portion and a shaft portion whose width is equal to or smaller than the width of the terminal portion, a coil spring permitting the shaft to be inserted therein, and a second plunger having an U-shape section, to be connected with the contact terminal of the external circuit.
Further, each of the contact pins may be formed with a plunger, including a terminal portion to be in contact with the external terminal of the IC package, a wider portion whose width is larger than the first terminal portion and a shaft whose width is equal to or smaller than the width of the first terminal portion, and a coil spring unit, including a coil spring permitting the shaft to be inserted therein, and a tight-winding coil portion following the coil spring.
Further, each of the contact pins may be formed with a first plunger, including a first terminal portion to be in contact with the external terminal of the IC package, a wider portion whose width is larger than the width of the first terminal portion and in which a fitting indent opening downward is disposed, and a second plunger, including a second terminal portion to be in contact with the contact terminal of the external circuit, and a pair of legs extending upward from the second terminal portion to fit in the fitting indent and having elastically deformable bent portions provided at the middle of the legs.
Furthermore, each of the contact pins may be formed with a first plunger, including a first terminal portion to be in contact with the external terminal of the IC package, a wider portion whose width is larger than the width of the first terminal portion and provided with a pair of legs extending downward from the two sides of the wider portion, a second plunger, including a second terminal portion to be connected with the contact terminal of the external circuit and an extended portion extending upward from the second terminal portion and slidably interposed between the pair of the legs of the wider portion and a coil spring interposed between the pair of the legs.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.